Inverters are high voltage electrical equipment, responsible for the frequency variation of the machines, used in several drives of equipment in a plant, containing mostly a fan with a motor.
Faults in this type of motor, such as bearing failures, unbalance, and mechanical looseness compromise the entire thermal exchange by stopping the fan. Therefore, motor stoppages increase the temperature of the inverters’ internal components.
Below, see how the technology was applied in this equipment, supporting the inspection activity and optimizing the fault prognosis in the plant’s ventilation system.
The risks with electricity and the occurrences of shutdowns caused by high temperatures in an inverter of the Power Flex 7000 model, installed in Carajás, was the starting point for the remote sensing project in panels of the electrical room.
Because of the fault, the ventilation system’s function of cooling the drive’s electronic components was not being carried out. As a result, stopping the fan brings the drive to a standstill, which ultimately impairs the entire operation.
Therefore, the work done on the Power Flex 7000 inverters aimed to eliminate unexpected shutdowns, caused by failures in the ventilation system, forced by the inverter itself as a protection measure.
In turn, the constructive form of this inverter model does not allow access to the fan, which makes quality inspection and even maintenance difficult.
Due to the high voltage and no access to the motor housings, the vibration collections were made on the external structure of the panel, using a vibration pen measuring only the global level. But this condition did not guarantee the predictability of the failure.
Another negative point was the inspector’s exposure to electrical risk, since the inspection depended on opening the panel to collect vibration with the machine in full operation.
Given the situation, Vale’s inspection team contacted the Specialized Predictive Technician, Antônio Andrade, to suggest other types and ways of vibration analysis that did not require opening the panel with the equipment working.
“The idea quickly came to me to put Dynamox’s wireless sensor there! We glued the sensor to the fan motor and started to monitor the two bearings and the dynamic condition”.
After installation, the sensors were configured to measure and save to internal memory the overall vibration and temperature level every 30 minutes. In addition to waveform collection and conversion to vibration spectra.
The collections previously performed by vibration pen, gave place to cell phone and tablet with bluetooth communication, eliminating any risk of inspectors’ exposure.
The main result was safety for the inspection team, which previously had to wear blasting suits to open the panel and perform measurements on the equipment.
In addition, there were also gains in terms of optimization of diagnostic values, since the old ones were inconsistent.
For Andrade, the sensor glued on the machine made the difference for a more assertive and safer collection. Want to learn more about how to obtain reliable data with wireless sensors and their attachment methods? Read this article here.
Since the first measurement there were open reports for unbalance correction on fan rotor blades, as signaled in the before and after in the speed spectrum graphs below.
In it, one can see the reliability of the vibration levels, making it possible to monitor the equipment without the need to open or measure directly on the casing.
For Felipe Pimenta, Predictive Technician II, “the gains in predictability of fan failure were enormous. This is a pioneering type of monitoring in the plant, because frequency inverters are hardly ever monitored. In Carajás it was an innovative project, the main result was the safety for the inspection team and the reduction of unexpected shutdowns”.
Besides this project, more sensors are being installed in similar equipment at the Carajás plant, as a result of the application results.
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